Researchers Put the "Five Second Rule" to the Test

It's a line often uttered in elementary lunchrooms and cafeterias worldwide. A food drops on the floor and you hear, "Five second rule!" The idea is that food isn't contaminated if it is dropped and then picked up off of the floor quickly.

According to the Daily Mail, the Manchester Metropolitan University decided to test out the famous rule to see if this common way of handling fallen food was actually a science. The study included five different foods, which were each dropped and left on the floor for three, five, and ten second intervals.

The foods chosen for the study were bread with jam, cooked pasta, ham, a plain biscuit, and dried fruit — all commonly eaten items that have different water levels, which contributes to bacterial growth.

After the initial dropping of the food, the morsels were examined to see if harmful bacteria was present. The study ultimately showed that foods with a high salt and sugar content are safest under the "five second rule." The ham and bread with jam performed well after being dropped for three seconds. The biscuits were also deemed safe to eat after a full five or ten seconds, probably because of their low water content.

The dried fruit and cooked pasta did not fare as well. Klebsiella, a bacteria which can lead to pneumonia, septicaemia, and urinary tract infections was present in both items after just three seconds on the floor.

Ultimately, there are two factors to take into account when practicing the "five second rule": the food and the floor. According to the study, if the food has a low water content and is high in salt and sugar, then there's a higher chance that the "five second rule" is safe. However, if the food has a high water content the danger level increases. Additionally, if the food falls onto a surface that is cleaned relatively often, the chance of bacteria decreases. If the floor is extremely dirty, the "five second rule" probably won't apply.